For detection of pulse waves, various methods including a method by which a heart rate is obtained by directly detecting results of electrocardiographic monitoring and a method by which a blood flow pitch is measured on the basis of the reflection light or transmitted light obtained by irradiating a blood vessel with light are used. The latter method imposes less burden of wearing the equipment on the examinees.
As a conventional method of measuring pulse rates, a method in which an average of input signals is calculated in prescribed units and a Fourier transform is performed on the resultant value is known. This method permits accurate measurement of pulse rates even with operation means of a low computing capacity.
As a conventional method relating to electronic sphygmomanometers, a method in which only limited heart rates are used for calculating an average of pulse wave pitches is known. In this method, it is determined whether or not a pulse wave pitch of a newly obtained pulse wave is equal to the average pulse wave pitch, and a counter value is incremented when it is not equal. When the counter value has reached a prescribed value, generation of too much noise is recognized and a signal reporting this fact is transmitted.
Further, as a conventional method of smoothing waveforms, a method in which ε filter is used is known. In this method, an average value is used for reducing fluctuation when the waveform is in a stationary state, and when the waveform is in a transient state, the waveform itself is output in order to eliminate phase delays.    Patent Document 1:
Japanese Laid-open Patent Publication No. 2004-121625    Patent Document 2:
Japanese Laid-open Patent Publication No. 01-190335    Patent Document 3:
Japanese Laid-open Patent Publication No. 2004-150280